so it would make sense be able to resize windows while keeping a tiled layout.
E.g. in this case i would manually resize the small terminal to lets say 20% and therefore
implicitly the pdf viewer to 80%.

So if i open a new window on this tag, it will still get 33% like it does now, but the
remaining 67% are now also distributed with those manual resize hints ->

This would also work when closing a window. So by resizing a window manually (or maybe even
with rules in the config file), you basically just say:
I want this window to be bigger/smaller then average and awesome would still be dynamic but just
takes these manual hints into account.

It was very simple in ion, there were bindings to grow and shrink the current client in any direction that made sense. I'm not sure what this means for the implementation, but currently I think tiling mode resizing is restricted and non-intuitive

@Midare: In ion, it was much easier because there were static layouts, awesome uses dynamic layouts which makes things harder. However, it should also be possible in awesome, as calmar's patch demonstrated.